The Background section of this document is provided to place embodiments of the present disclosure in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.
Cellular communication systems are currently being developed and improved for machine type communication (MTC), which is a type of communication characterized by lower demands on data rates than for example mobile broadband, but with higher requirements on e.g. low cost device design, better coverage, and ability to operate for years on batteries without charging or replacing the batteries. Currently, Third Generation Partnership Project (3GPP) is standardizing a feature called Narrowband Internet of Things (NB-IoT) for satisfying all the requirements put forward by MTC type applications, while maintaining backward compatibility with the current Long Term Evolution (LTE) radio access technology. A new work item named Narrowband IoT (NB-IoT) has been approved in 3GPP where the objective is to specify a radio access for cellular internet of things that addresses improved indoor coverage, support for massive number of low throughput devices, low delay sensitivity, ultra-low device cost, low device power consumption and (optimized) network architecture.
NB-IoT systems have three different deployment modes, i.e., stand-alone, guard-band, and in-band. In stand-alone mode, the NB-IoT system is operated in dedicated frequency bands. For in-band operation, the NB-IoT system can be placed inside the frequency bands used by the current LTE system by using one or several LTE Physical Resource Block (PRB) for NB-IoT systems, while in the guard-band mode, the NB-IoT system can be placed in the frequency band used as guard band by the current LTE system. The NB-IoT has a system bandwidth of 180 kHz.
A channel raster of e.g. the downlink (DL) of NB-IoT systems is on a frequency grid of 100 kHz, also denoted cell search grid. That is, the NB-IoT devices try to find the NB-IoT carriers in a step size of 100 kHz. For the standalone deployment, this is fine. But for the in-band and guard-band operation, as observed in R1-160082, NB-IoT Channel Raster, source Ericsson, 3GPP TSG-RAN1 NB-IOT Ad Hoc 18-20 Jan. 2016, Budapest, Hungary, there is no LTE PRB that can be used for NB-IoT deployment that falls directly on the cell search grid used for NB-IoT in LTE in-band operation. The frequency offset to the 100 kHz grid is a minimum of ±2.5 kHz and ±7.5 kHz for even and odd number of PRBs in the LTE system bandwidth, respectively (see R1-160082, NB-IoT Channel Raster, source Ericsson, 3GPP TSG-RAN1 NB-IOT Ad Hoc 18-20 Jan. 2016, Budapest, Hungary). The ±2.5 kHz or ±7.5 kHz can be handled by the wireless device during the cell search process and then compensated for. However, these channel raster offsets constrain the positions where NB-IoT carriers can be deployed for the in-band and guard-band operations.
For the guard-band operation, for an LTE system with 10 or 20 MHz system bandwidth, it is possible to find e.g. NB-IoT downlink carrier frequency that is 2.5 kHz off the 100 kHz channel raster. For other LTE system bandwidths, the offset to the 100 kHz raster is 52.5 kHz. Therefore, in order to get within the same ±7.5 kHz to the 100 kHz grid, 3 guard subcarriers are needed. One guard carrier is of a 15 kHz width and placed in the same Fast Fourier Transform (FFT) grid at the legacy LTE system that gives orthogonality to the legacy LTE PRB. However, there are no other solutions to put the NB-IoT carriers on the exact 100 kHz raster grids in the LTE guard-band without losing orthogonality to the legacy LTE system. If an NB-IoT system is deployed in the guard-band of an LTE system and not orthogonal to the LTE subcarriers, e.g., to fulfill the 100 kHz channel raster requirement, the existing solution is either to transmit the NB-IoT carrier at a lower power or to use stringent channel filters to ensure that the LTE spectrum mask, which regulates out of band emission levels, is not violated and that there is no significant interference between the NB-IoT system and the LTE system.
Thus, it may be rather resource consuming or resource inefficient, according to prior art, to enable the wireless device to use a first wireless communication system, such as an NB-IoT system, that is deployed together with a second wireless communication system such as a LTE system.